The mechanisms underlying the pathogenesis of fever in man are a major area of interest. Present investigations are directed at: (1) purification of human leukocytic pyrogen; and (2) development of a radioimmunoassay for human leukocytic pyrogen. Receiving equal attention and effort are some of the mechanisms responsible for nonspecific resistance to infection. Inducers of resistance such as bacterial endotoxins, other bacterial products and synthetic adjuvants are under study.